A typical freight train includes one or more locomotives, a plurality of railcars and a pneumatic trainline referred to as a brake pipe. The brake pipe consists of a series of individual pipe lengths interconnected to each other. One pipe length secured to the underside of each railcar interconnects to another such pipe length via a flexible coupler situated between each railcar. The brake pipe supplies the pressurized air that is required by the brake control system to charge the various reservoirs and operate the air brake equipment on each railcar in the freight train.
A train operator situated in the lead locomotive can manipulate a brake handle to apply and release the brakes on the railcars as desired. The brake handle can be moved from and in between a release position at one extreme in which brake pipe pressure is maximum and the brakes are completely released to an emergency position at another extreme in which brake pipe pressure is minimal and the brakes are fully applied. The brake handle positions thus include brake release, minimum service brake application, full service brake application and emergency brake application. When the brakes are released, the reservoirs and the brake pipe are generally charged to the same pressure: typically 90 psi on a freight train and 110 psi on a passenger train. When the brakes are applied, the pressure in the brake pipe is reduced via a valve located in the lead locomotive. The exact amount by which the pressure is reduced depends into which of the application positions the brake handle is placed. It is this pressure reduction that signals the brake control valve on each railcar to supply pressurized air from the appropriate reservoir(s) to the brake cylinders. The brake cylinders convert this pressure to the mechanical force that the brake shoes apply to slow or stop the rotation of the wheels on the railcar. Assuming the brake signal is successfully communicated throughout the train, the brakes of all railcars in the train respond in generally the same manner.
FIG. 1 illustrates a schematic diagram of the air brake equipment of a typical freight railcar equipped with empty and load brake equipment. The air brake equipment typically includes one or more brake cylinders, an emergency air reservoir, an auxiliary air reservoir and an "ABD" or similar type pneumatic brake control valve. The operation of the pneumatic control valve as well as a description of its components is provided in the aforementioned copending application.
Each freight railcar may include empty and load brake equipment such as a P-1 load proportional valve and an S-1 type or an ELX type load sensor valve all of which are made by the Westinghouse Air Brake Company (WABCO) and are well known in the brake control art. The objective of empty and load brake equipment is to reduce braking on the railcar if it is empty and to permit heavier braking on the railcar if it is loaded. On a freight train with railcars equipped with empty and load brake equipment, the braking is more uniformly applied throughout the train in accordance with the load borne by the railcars. This tends to reduce the slack between adjacent railcars and improves overall handling of the freight train.
Regarding the operation of a load sensor valve, the S-1 load sensor valve, for example, automatically senses whether the railcar is loaded or empty generally by measuring the relationship between the body of the railcar and the top of the side frame of the truck. Each railcar typically has two trucks, one at each end. Each truck includes the wheels and axles and other parts that together form the structure that supports the body of the railcar. Suspension springs are used to dampen vibrations that would otherwise be transmitted from the wheels to the railcar body and that may otherwise damage the load being transported. These suspension springs deflect or compress to an extent proportional to the weight of the load carried by the railcar.
Typically mounted to the underside of the railcar body, the S-1 load sensor valve uses its sensor arm to measure the distance between the railcar body and the top of the truck side frame. When loaded, the railcar body further compresses the springs thereby reducing the distance between the railcar body and the truck side frame. The distance that the sensor arm can travel is therefore limited. Conversely, when the railcar is empty, the springs are less compressed thereby maximizing the distance between the railcar body and the truck side frame. The distance that the sensor arm can travel is then at its maximum.
When the S-1 load sensor senses that the railcar is empty, its internal mechanism serves to regulate the flow of air to the P-1 load valve. When the railcar is empty, the P-1 load proportional valve controls the flow of air to the brake cylinder so that the brake cylinder pressure is approximately 60% of what it would be if the railcar were loaded no matter how much the pressure is reduced in the brake pipe. During brake applications, the equalizing volume is used to maintain a satisfactory relationship between pressure in the empty and load brake equipment and that in the control valve and its reservoirs when the railcar is empty. Empty and load brake equipment such as the type alluded to in this document is described in U.S. Pat. Nos. 5,005,915 and 5,100,207. These patents are assigned to the assignee of the present invention, and their teachings are incorporated into the present document by reference.
Whether of the S-1 type or ELX type, the load sensor valve features one or more internal chambers or passageways. An interconnecting pipe connects at least one of these chambers or passageways to the brake cylinder as shown, for example, in the schematic diagram of FIG. 1. An S-1 load sensor valve of the type shown schematically in FIG. 1 is illustrated in FIG. 2. The left side of the housing of the load sensor valve features a generally cylindrical portion flanked by two bolts. Between these bolts and screwed into a threaded bore in the cylindrical portion is a pipe plug. Removal of the pipe plug provides direct access to the chamber that communicates with the brake cylinder via the interconnected pipe shown in FIG. 1. The threaded bore in the housing can thus be used as an access port through which to access the pressure in the brake cylinder from the load sensor valve.
The American Association of Railroads (A.A.R.) has proposed that each railcar of a freight train be provided with a mechanism that would allow the pressure within the brake cylinder to be read quickly. At present, the A.A.R. is considering whether to issue a specification requiring that a commercially available quick connect type fitting be used to access the pressure within the brake cylinder. The disadvantage of such a fitting, however, is that it provides only a single seal with which to contain the pressure to be measured. That is, while such a fitting is not being used to access the pressure, it offers only one seal to prevent leakage of the pressure that it is supposed to contain. Unless the fitting is routinely covered to protect the seal when the fitting is not being used to access the brake cylinder pressure, the seal is exposed to dust, dirt and/or other potential contaminants. It is, of course, important that such a fitting prevent leakage of pressure from the brake cylinder otherwise operation of the brakes may be adversely affected.
It should be noted that the foregoing background information is provided to assist the reader in understanding the instant invention. Accordingly, any terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.